| Abstract: | When fertilization of developing cereal grains occurs, the pericarp (ovary wall) already contains starch granules. Hence the starch content of developing grains of wheat, triticale, rye, oats and barley commences at 30 or 40% of the dry weight. It increases only to 60 or 70% at ripeness when the pericarp has degenerated to bran layers and the endosperm is filled with stored starch granules and protein. All these cereals showed similar patterns of starch increase, with an inflexion at 40 to 50% starch due to degeneration of pericarp starch before endosperm deposition. In wheats and triticale there was a second inflexion at 50 to 60% starch caused by endosperm cells proliferating faster than they filled with starch granules. The rise and fall of rate of starch deposition coincided with the rise and fall of percentage of metabolic (non-storage) protein in the grain, calculated from total amino acid analyses. In the mature grain about 8% of the dry matter is not associated with starch and thus is non-endosperm tissues. About 70% of the remaining dry matter (endosperm) is starch. We suggest that fluctuations of metabolites and enzymes result from development or breakdown of groups of cells constituting distinct tissues in the grain. |
